diff --git a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.S7/S7Driver.cs b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.S7/S7Driver.cs
index 972aee74..f5f7f7af 100644
--- a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.S7/S7Driver.cs
+++ b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.S7/S7Driver.cs
@@ -590,7 +590,7 @@ public sealed class S7Driver
internal static int ScalarByteWidth(S7TagDefinition tag) => tag.DataType switch
{
S7DataType.Int64 or S7DataType.UInt64 or S7DataType.Float64 => 8,
- S7DataType.DateTime => 8,
+ S7DataType.DateTime => 8, // 8 = S7 DATE_AND_TIME/DT BCD (S7.Net.Types.DateTime; the 8-byte DT, not 12-byte DTL).
S7DataType.String => tag.StringLength + 2,
_ => throw new InvalidOperationException(
$"S7 ScalarByteWidth called for non-buffer type {tag.DataType} (tag '{tag.Name}')"),
@@ -623,8 +623,11 @@ public sealed class S7Driver
// padding past curLen — it validates curLen against the block, so no extra guard is needed.
S7DataType.String => global::S7.Net.Types.S7String.FromByteArray(block),
- S7DataType.DateTime => throw new NotSupportedException(
- "S7 DateTime scalar reads land in a follow-up PR"),
+ // S7 classic DATE_AND_TIME (DT): 8-byte BCD value (year/month/day/hour/min/sec + ms +
+ // day-of-week nibble). S7.Net's DateTime.FromByteArray reads the BCD fields and returns a
+ // System.DateTime; the DT range is 1990–2089 and round-trips to the millisecond. Boxed as
+ // System.DateTime explicitly (the cast pins the box type, consistent with the numeric arms).
+ S7DataType.DateTime => (object)global::S7.Net.Types.DateTime.FromByteArray(block),
_ => throw new System.IO.InvalidDataException(
$"S7 scalar Read type-mismatch: tag '{tag.Name}' declared {tag.DataType} but address " +
@@ -673,7 +676,11 @@ public sealed class S7Driver
return global::S7.Net.Types.S7String.ToByteArray(Convert.ToString(value) ?? "", tag.StringLength);
case S7DataType.DateTime:
- throw new NotSupportedException("S7 DateTime scalar writes land in a follow-up PR");
+ // S7.Net's DateTime.ToByteArray builds the 8-byte DT BCD block. It validates the
+ // 1990–2089 DT range and throws ArgumentOutOfRangeException for an out-of-range year —
+ // we surface that (no silent clamp). Value coerced via Convert.ToDateTime (accepts a
+ // System.DateTime or a parseable timestamp string).
+ return global::S7.Net.Types.DateTime.ToByteArray(Convert.ToDateTime(value));
default:
throw new InvalidOperationException(
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.S7.Tests/S7ScalarBlockTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.S7.Tests/S7ScalarBlockTests.cs
index 736f5b65..b408a326 100644
--- a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.S7.Tests/S7ScalarBlockTests.cs
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.S7.Tests/S7ScalarBlockTests.cs
@@ -12,8 +12,10 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.S7.Tests;
/// network I/O half (Plc.ReadBytesAsync/WriteBytesAsync) has no in-process
/// fake so only the codec is unit-proven (mirrors ).
/// String (S7 classic STRING) decode/encode is proven here via
-/// ; DateTime decode is still a deferred stub (T4) and
-/// this file pins the NotSupportedException contract it lands against.
+/// ; DateTime (S7 classic DATE_AND_TIME / DT, 8-byte BCD)
+/// decode/encode is proven via (the 8-byte DT helper —
+/// NOT DTL). Timer/Counter decode/encode are still deferred stubs (T5) and this file pins the
+/// NotSupportedException contract they land against.
///
[Trait("Category", "Unit")]
public sealed class S7ScalarBlockTests
@@ -296,19 +298,74 @@ public sealed class S7ScalarBlockTests
decoded.ShouldBeOfType().ShouldBe("ABCDE");
}
- // ── Deferred-stub contract: DateTime throws NotSupportedException ──────────────────────
+ // ── DecodeScalarBlock — DateTime (S7 classic DATE_AND_TIME / DT) ───────────────────────
- /// Verifies DateTime decode is a deferred stub (NotSupportedException — T4).
+ /// Verifies an 8-byte S7 DT block decodes to its value
+ /// via (the 8-byte BCD DT helper, not the 12-byte DTL).
[Fact]
- public void DecodeScalarBlock_DateTime_throws_NotSupported()
+ public void DecodeScalarBlock_DateTime_reads_dt_bcd_block()
{
- var tag = Tag(S7DataType.DateTime);
- var block = new byte[S7Driver.ScalarByteWidth(tag)];
- Should.Throw(() => S7Driver.DecodeScalarBlock(tag, Addr(), block));
+ var expected = new System.DateTime(2026, 6, 17, 12, 34, 56);
+ // Fixture built by S7.Net's own DT encoder so the block matches the on-the-wire DT layout.
+ var block = global::S7.Net.Types.DateTime.ToByteArray(expected);
+ block.Length.ShouldBe(8);
+
+ var result = S7Driver.DecodeScalarBlock(Tag(S7DataType.DateTime), Addr(), block);
+ result.ShouldBeOfType().ShouldBe(expected);
}
- /// Verifies DateTime encode is a deferred stub (NotSupportedException — T4).
+ // ── EncodeScalarBlock — DateTime ───────────────────────────────────────────────────────
+
+ /// Verifies a encodes to an 8-byte DT block.
[Fact]
- public void EncodeScalarBlock_DateTime_throws_NotSupported()
- => Should.Throw(() => S7Driver.EncodeScalarBlock(Tag(S7DataType.DateTime), "x"));
+ public void EncodeScalarBlock_DateTime_writes_eight_byte_block()
+ {
+ var value = new System.DateTime(2026, 6, 17, 12, 34, 56);
+ var block = S7Driver.EncodeScalarBlock(Tag(S7DataType.DateTime), value);
+ block.Length.ShouldBe(8);
+ // Matches S7.Net's own DT encoder exactly (same on-the-wire bytes).
+ block.ShouldBe(global::S7.Net.Types.DateTime.ToByteArray(value));
+ }
+
+ /// Verifies a string/ISO timestamp coerces via Convert.ToDateTime before encoding.
+ [Fact]
+ public void EncodeScalarBlock_DateTime_coerces_string_value()
+ {
+ var tag = Tag(S7DataType.DateTime);
+ var block = S7Driver.EncodeScalarBlock(tag, "2026-06-17T12:34:56");
+
+ var decoded = S7Driver.DecodeScalarBlock(tag, Addr(), block);
+ decoded.ShouldBeOfType().ShouldBe(new System.DateTime(2026, 6, 17, 12, 34, 56));
+ }
+
+ /// Verifies a year outside the S7 DT range (1990–2089) throws — S7.Net's DT encoder
+ /// validates the range and raises ; we surface it.
+ [Theory]
+ [InlineData(1980)]
+ [InlineData(2100)]
+ public void EncodeScalarBlock_DateTime_out_of_range_year_throws(int year)
+ {
+ var tag = Tag(S7DataType.DateTime);
+ var value = new System.DateTime(year, 1, 1, 0, 0, 0);
+ Should.Throw(() => S7Driver.EncodeScalarBlock(tag, value));
+ }
+
+ // ── DateTime round-trip identity (encode → decode) ────────────────────────────────────
+
+ /// Verifies DateTime round-trips through encode→decode. S7 DT preserves full
+ /// millisecond precision (the 8-byte BCD packs ms-tens/hundreds), so the identity holds to
+ /// the millisecond — no precision loss to document below the second.
+ [Theory]
+ [InlineData(1990, 1, 1, 0, 0, 0, 0)] // DT minimum.
+ [InlineData(2026, 6, 17, 12, 34, 56, 0)] // no sub-second.
+ [InlineData(2026, 6, 17, 12, 34, 56, 789)] // milliseconds preserved.
+ [InlineData(2089, 12, 31, 23, 59, 59, 999)] // DT maximum, ms boundary.
+ public void DateTime_round_trips_to_the_millisecond(
+ int y, int mo, int d, int h, int mi, int s, int ms)
+ {
+ var value = new System.DateTime(y, mo, d, h, mi, s, ms);
+ var tag = Tag(S7DataType.DateTime);
+ var decoded = S7Driver.DecodeScalarBlock(tag, Addr(), S7Driver.EncodeScalarBlock(tag, value));
+ decoded.ShouldBeOfType().ShouldBe(value);
+ }
}